The present invention relates to uninterruptible power supply (UPS) systems and, more particularly, to power supplies that generate an AC power signal based on a selected one of a plurality of power sources.
Electronic equipment is conventionally designed to operate on an alternating current power signal distributed by a public utility. The AC power signal is presumed to be present at all times and to be within certain predetermined parameters. If the AC power signal is not present, is disrupted, or does not fall within the predetermined parameters, the electronic equipment may fail to operate and/or operate unreliably. In such situations, the electronic equipment will be unable to perform its intended purpose.
UPS systems are often used in conjunction with certain electronic equipment to ensure the presence of an AC power signal that is within the required predetermined parameters. For example, telecommunications equipment, CATV equipment, and computers are often protected to some degree by UPS systems.
UPS""s commonly create or pass an AC power signal from a first power source (the xe2x80x9clinexe2x80x9d signal) and generate the AC power signal from a second power source (the xe2x80x9cstandbyxe2x80x9d signal) when the first power source is disrupted. Commonly, the first power source is a utility power supply system, and the second power source is a battery or engine/generator that operates only when the utility power system is disrupted.
The need exists for efficient, reliable UPS systems that use the least expensive energy source available.
The following patents were uncovered as part of a professional patentability search conducted on-behalf of the Applicant.
U.S. Pat. No. 6,011,324 issued to Kohistruck et al. discloses an uninterruptible power supply that operates based on either a line voltage or an electrical signal generated by a fuel cell and a current inverter.
U.S. Pat. No. 5,880,536 issued to Mardirossian discloses a fuel cell adapted for use by a consumer to supplement the electrical power provided by a utility power source.
U.S. Pat. No. 5,783,932 issued to Namba et al. discloses a power generation plant that employs a fuel cell to provide power when regenerative energy provided by a load commutated inverter can no longer be sustained.
U.S. Pat. No. 4,890,213 to Seki discloses a power converter that limits the voltage induced in d.c. windings of a transformer.
U.S. Pat. No. 4,775,800 to Wood discloses a power supply including a battery connected between a generator such as a fuel cell and a load. The battery stores energy when the energy supplied by the generator exceeds that required by the load.
U.S. Pat. No. 4,700,122 to Cimino et al. discloses a battery connected between a DC energy source and a load to filter the signal generated by the energy source.
U.S. Pat. No. 4,670,702 to Yamada et al. discloses a controller for a fuel cell power system. The controller employs switching elements to charge a battery in different modes depending upon the status of the fuel cell.
U.S. Pat. No. 4,472,641 discloses circuitry for combining power signals generated by a plurality of power modules of differing characteristics.
U.S. Pat. No. 4,251,736 discloses a force-commutated inverter that is arranged between an electrochemical cell and a power grid for adjusting the real and reactive power components of an AC power signal.
U.S. Pat. No. 3,823,358 to Rey discloses the use of a battery in parallel with a fuel cell to supply additional current when the demand of a load causes the voltage of the fuel cell to drop.
The following United States patents issued to the assignee of the present application relate to power supplies, some of which generate power signals based on separate power sources.
U.S. Pat. No. 6,014,015 to Thorne discloses a power supply that employs an internal combustion engine to generate an AC power signal.
U.S. Pat. No. 5,961,015 to Anderson et al. discloses a system for monitoring the status of components in a distributed system such as a communications system.
U.S. Pat. No. 5,892,431 to Osterman discloses a power multiplexer for use in broadband communications systems.
U.S. Pat. No. 5,760,495 to Mekanik discloses an inverter/charger circuit for use in uninterruptible power supplies.
U.S. Pat. Nos. 5,739,595 to Mekanik et al. and 5,410,720 to Osterman disclose power supplies that generate a waveform optimized for use in cable TV distribution systems.
U.S. Pat. Nos. 5,642,002 and 5,638,244 to Mekanik et al. disclose uninterruptible power supplies operating in line mode using utility power and in a standby mode using battery power.
The present invention may be embodied as an uninterruptible power supply system comprising a source of a utility power signal, a source of hydrogen, a fuel cell stack, first and second input circuits, an output circuit, and a control circuit. The fuel cell stack converts the hydrogen into a fuel cell output signal. The first input circuit is operatively connected to the utility power signal and outputs a first AC input signal based on the utility power signal. The second input circuit operatively is connected to the fuel cell output signal and generates a second AC input signal based on the fuel cell output signal. The output circuit is operatively connected to the first and second input circuits and outputs at least one output signal based on one of the first and second AC input signals. The control circuit operatively is connected to the fuel cell stack, the first input circuit, the second input circuit. The output circuit controls whether the output signal is generated based on the utility power signal or hydrogen.
Preferably, the present invention employs a switch-mode dc-to-dc voltage regulator to regulate the slow and rapid dynamics of the voltage obtained from the fuel cell stack. This switching voltage regulator operates with significant voltage ripple from the fuel cell stack.
The present invention may also be embodied as a system with a fuel cell used in continuous operation to provide power to an integrated electric power converter. This produces a very reliable system since the voltage and power delivered from the fuel cell to the electric power converter is not exposed to the potentially-destructive transients which are present on the utility electric lines.
The fuel cell and reformer control systems may need to respond differently in a system with a battery available as one of the power sources. The present invention may thus also be embodied as a system where the presence or absence of a battery is determined through any of several methods, including step response. The control algorithm for the fuel cell and fuel processor is based on the presence or absence of a battery. With no battery, the fuel cell is commanded on regardless of fuel cell output voltage. With battery present, the fuel cell is turned on at some minimum battery voltage and off at some maximum battery voltage.
The present invention has many applications but is of particular significance when implemented as a fuel cell system for powering a cable TV outside plant system.
The present invention may also be implemented using a fuel cell system which is a reformer-based system having a reserve of hydrogen to allow for instantaneous startup and rapid load dynamics. The use of such a reserve may eliminate the need for batteries.